The present disclosure relates to a positively chargeable toner for electrostatic image development and a developer containing the same.
In electrophotographic devices, electrostatic latent images formed on photoreceptors from developing machines using a developer containing toner are visualized by using toner and the visualized images are then transferred onto transfer bodies followed by fixation of the images onto transfer materials such as paper sheets by means of heat in order to obtain images. Full colour images can be obtained by using four toners, i.e., black, yellow, magenta and cyan and overlaying the respective toner images.
However, electrophotographic images have not reached to a satisfactory level in terms of image quality compared to high-quality images such as silver halide photography and printed matters. Therefore, further improvements in quality of images and reliability thereof are required, and it is sought to confer with toner particles reduced diameters, uniform shapes and improved charge stability and to confer with toner narrow and stable particle size distribution.
In addition, because of an increased interest about energy saving performances and environment protecting performances, toner is sought to be manufactured with materials and methods which allow fixation at decreased temperatures and have decreased impacts on the environment.
In order to achieve these aims, toner particles are required to be prepared by the method that allows the design of toner particles having desired shape and size and the structural design of the particles so that toner materials are arranged in terms of position and condition so as to be able to exhibit the maximum performances thereof.
In order to fulfil the above requirement, conventional pulverization methods in which a binder resin, a colorant, a charge controlling agent, wax and the like for toner are mixed and then pulverized have been replaced by chemical methods in which toner particles containing a colorant, a charge controlling agent, wax and the like are built up from fine particles by polymerization of monomers or by particle growth from polymers.
In such procedures, it has been reported that toner having a hydrophobicity of 30% or less can provide stable and high density printing images even after continuous printing on a high-speed image forming apparatus, cause no image fogging even after a high amount of printing and reduce scattering of the toner in the apparatus.
Among others, an emulsion aggregation method in which emulsified fine particles of materials for toner are aggregated and melt-adhered for granulation is the most ideal granulation method because the shape and particle diameter distribution of particles can be easily controlled and the structure of particles can also be controlled.
It has been reported that the emulsion aggregation toner includes crystalline polyester fine particles and wax fine particles, the crystalline polyester has a weight average molecular weight Mw of 1000 or more and 5000 or less, the wax component has a melting point of 45 to 75° C. and the toner has the methanol concentration (% by volume) of 30 to 70% at the transmittance of 50% in methanol wettability. The toner has significantly improved developing properties in terms of development streaks and fogging and improved fixing performances in terms of image frictional properties and image peeling.